[AZ-Observing] Re: Pleiades Occultation
- From: Tom Polakis <tpolakis@xxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Fri, 14 Aug 2009 15:15:52 -0400
---- Randy Peterson <rgpeterson@xxxxxxx> wrote:
> The largest magnitude drop of the 32 predicted events is on September 30
> starting about 00:05 am, +/- 48 seconds. Io will eclipse Europa again. It
> is predicted to drop over 1 magnitude, which may be visible visually. The
> duration of this event is a bit over 8 minutes. More at
> http://www.hristopavlov.net/SatWatcher/2009-9-30-7-9-56-Io(I)_Europa(II).html
Randy,
Thanks for the link to that SatWatcher site. The illustrations are very good.
I wonder how the magnitude drop can be any larger than 0.75, though. What I
remember about unresolved double stars is that if you combine the brightness of
the two stars, the maximum increase is 0.75, and that's for two identically
bright stars. For example, the combined brightness of two 3rd-magnitude stars
is 2.25. If the two stars are 2nd and 3rd magnitude, the combined brightness
is 1.64, or only 0.36 magnitudes brighter than the single 2nd-magnitude star.
I will have to ask the author of that Web site, who seems to know his stuff.
Here's a fun little equation for combined brightness of unresolved stars to
play with after a couple beers.
m(sum) = m1 -2.5 log {1 + antilog[ -0.4 (m2 - m1)]}
where:
m(combined) = combined magnitude
m1 and m2 are the magnitudes of the unresolved stars
--
See message header for info on list archives or unsubscribing, and please
send personal replies to the author, not the list.
Other related posts:
